The present invention relates to body fluid testing devices and more specifically, but not exclusively, concerns a body fluid testing device that incorporates a test media cassette which contains test media used to test body fluid.
General Fluid Testing
The acquisition and testing of body fluids is useful for many purposes and continues to grow in importance for use in medical diagnosis and treatment and in other diverse applications. In the medical field, it is desirable for lay operators to perform tests routinely, quickly and reproducibly outside of a laboratory setting, with rapid results and a readout of the resulting test information. Testing can be performed on various body fluids, and for certain applications is particularly related to the testing of blood and/or interstitial fluid. Such fluids can be tested for a variety of characteristics of the fluid, or analytes contained in the fluid, in order to identify a medical condition, determine therapeutic responses, assess the progress of treatment, and the like.
General Test Steps
The testing of body fluids basically involves the steps of obtaining the fluid sample, transferring the sample to a test device, conducting a test on the fluid sample, and displaying the results. These steps are generally performed by a plurality of separate instruments or devices.
Acquiring—Vascular
One method of acquiring the fluid sample involves inserting a hollow needle or syringe into a vein or artery in order to withdraw a blood sample. However, such direct vascular blood sampling can have several limitations, including pain, infection, and hematoma and other bleeding complications. In addition, direct vascular blood sampling is not suitable for repeating on a routine basis, can be extremely difficult, and is not advised for patients to perform on themselves.
Acquiring—Incising
The other common technique for collecting a body fluid sample is to form an incision in the skin to bring the fluid to the skin surface. A lancet, knife, or other cutting instrument is used to form the incision in the skin. The resulting blood or interstitial fluid specimen is then collected in a small tube or other container, or is placed directly in contact with a test strip. The fingertip is frequently used as the fluid source because it is highly vascularized and therefore produces a good quantity of blood. However, the fingertip also has a large concentration of nerve endings, and lancing the fingertip can therefore be painful. Alternate sampling sites, such as the palm of the hand, forearm, earlobe, and the like, may be useful for sampling and are less painful. However, they also produce lesser amounts of blood. These alternate sites therefore are generally appropriate for use only for test systems requiring relatively small amounts of fluid, or if steps are taken to facilitate the expression of the body fluid from the incision site.
Various methods and systems for incising the skin are known in the art. Exemplary lancing devices are shown, for example, in U.S. Pat. Nos. Re 35,803, issued to Lange, et al. on May 19, 1998; 4,924,879, issued to O'Brien on May 15, 1990; 5,879,311, issued to Duchon et al. on Feb. 16, 1999; 5,857,983, issued to Douglas on Jan. 12, 1999; 6,183,489, issued to Douglas et al. on Feb. 6, 2001; 6,332,871, issued to Douglas et al. on Dec. 25, 2001; and 5,964,718, issued to Duchon et al. on Oct. 12, 1999. A representative commercial lancing device is the Accu-Chek® Softclix lancet.
Expressing
Patients are frequently advised to urge fluid to the incision site, such as by applying pressure to the area surrounding the incision to milk or pump the fluid from the incision. Mechanical devices are also known to facilitate the expression of body fluid from an incision. Such devices are shown, for example, in U.S. Pat. No. 5,879,311, issued to Duchon et al. on Feb. 16, 1999; 5,857,983, issued to Douglas on Jan. 12, 1999; 6,183,489, issued to Douglas et al. on Feb. 6, 2001; 5,951,492, issued to Douglas et al. on Sep. 14, 1999; 5,951,493, issued to Douglas et al. on Sep. 14, 1999; 5,964,718, issued to Duchon et al. on Oct. 12, 1999; and 6,086,545, issued to Roe et al. on Jul. 11, 2000. A representative commercial product that promotes the expression of body fluid from an incision is the Amira AtLast blood glucose system.
Sampling
The acquisition of the produced body fluid, hereafter referred to as the “sampling” of the fluid, can take various forms. Once the fluid specimen comes to the skin surface at the incision, a sampling device is placed into contact with the fluid. Such devices may include, for example, systems in which a tube or test strip is either located adjacent the incision site prior to forming the incision, or is moved to the incision site shortly after the incision has been formed. A sampling tube may acquire the fluid by suction or by capillary action. Such sampling systems may include, for example, the systems shown in U.S. Pat. Nos. 6,048,352, issued to Douglas et al. on Apr. 11, 2000; 6,099,484, issued to Douglas et al. on Aug. 8, 2000; and 6,332,871, issued to Douglas et al. on Dec. 25, 2001. Examples of commercial sampling devices include the Roche Compact, Amira AtLast, Glucometer Elite, and Therasense FreeStyle test strips.
Testing General
The body fluid sample may be analyzed for a variety of properties or components, as is well known in the art. For example, such analysis may be directed to hematocrit, blood glucose, coagulation, lead, iron, etc. Testing systems include such means as optical (e.g., reflectance, absorption, fluorescence, Raman, etc.), electrochemical, and magnetic means for analyzing the sampled fluid. Examples of such test systems include those in U.S. Pat. Nos. 5,824,491, issued to Priest et al. on Oct. 20, 1998; 5,962,215, issued to Douglas et al. on Oct. 5, 1999; and 5,776,719, issued to Douglas et al. on Jul. 7, 1998.
Typically, a test system takes advantage of a reaction between the body fluid to be tested and a reagent present in the test system. For example, an optical test strip will generally rely upon a color change, i.e., a change in the wavelength absorbed or reflected by dye formed by the reagent system used. See, e.g., U.S. Pat. Nos. 3,802,842; 4,061,468; and 4,490,465.
Blood Glucose
A common medical test is the measurement of blood glucose level. The glucose level can be determined directly by analysis of the blood, or indirectly by analysis of other fluids such as interstitial fluid. Diabetics are generally instructed to measure their blood glucose level several times a day, depending on the nature and severity of their diabetes. Based upon the observed pattern in the measured glucose levels, the patient and physician determine the appropriate level of insulin to be administered, also taking into account such issues as diet, exercise, and other factors. A proper control of the blood glucose level avoids hypoglycemia which may lead to insomnia and even sudden death as well as hyperglycemia resulting in long term disorders as blindness and amputations. Blood glucose is therefore a very important analyte to be monitored.
In testing for the presence of an analyte such as glucose in a body fluid, test systems are commonly used which take advantage of an oxidation/reduction reaction which occurs using an oxidase/peroxidase detection chemistry. The test reagent is exposed to a sample of the body fluid for a suitable period of time, and there is a color change if the analyte (glucose) is present. Typically, the intensity of this change is proportional to the concentration of analyte in the sample. The color of the reagent is then compared to a known standard which enables one to determine the amount of analyte present in the sample. This determination can be made, for example, by a visual check or by an instrument, such as a reflectance spectrophotometer at a selected wavelength, or a blood glucose meter. Electrochemical and other systems are also well known for testing body fluids for properties on constituents.
Testing Media
As mentioned above, diabetics typically have to monitor their blood glucose levels throughout the day so as to ensure that their blood glucose remains within an acceptable range. Some types of sampling devices require the use of testing strips that contain media for absorbing and/or testing the body fluid, such as blood. After testing, the testing media contaminated with blood can be considered a biohazard and needs to be readily disposed in order to avoid other individuals from being exposed to the contaminated test strip. This can be especially inconvenient when the person is away from home, such as at a restaurant. Moreover, individual test elements can become easily mixed with other test strips having different expiration dates. The use of expired test elements may create false readings, which can result in improper treatment of the patient, such as improper insulin dosages for diabetics.
Test Media Cassettes
Analytical systems with test media cassettes which allow multiple testing have been described in the prior art. There are available dispensers which contain a limited number of test elements; as for example, 1 to 2 dozen strips which are individually sealed. Blood glucose meter using such a test strip dispenser are in the market under the names AccuChek Compact (Roche Diagnostics GmbH) and DEX (Bayer Corporation). Consumers, however, demand systems that contain even more strips to reduce loading actions to be performed by the user. A suitable way to package a higher number of test elements are test films as e.g., described in U.S. Pat. No. 4,218,421 and U.S. Pat. No. 5,077,010. These test systems are, however, designed to be used in the environment of automated laboratory systems and are therefore not suited for patient self testing. DE 198 19 407 describes a test element cassette employing a test media tape for use in the patient self testing environment. A number of practical problems are, however, still unsolved when relying on the device described in DE 198 19 407. Test media used for blood glucose testing as well as for other analytes are prone to deterioration by humidity from the environmental air. It is therefore a serious problem to keep unused test media free from humidity to avoid deterioration which would lead to incorrect analytical results. U.S. Pat. No. 5,077,010 discloses containers for test media tape which have an outlet for the tape which is sealed by a blocking member or a resilient member (see in particular FIGS. 21 to 33 and corresponding disclosure). This way of sealing is comparable to the type of sealing known from photographic film boxes. The automated analytical instruments of U.S. Pat. No. 5,077,010 have a high throughput and therefore the required onboard stability is short (typically one or two days only). Contrary to that, the required onboard stability in the home diagnostic market is much longer. Considering a patient doing two testings a day and a test media capacity of a cassette in the range of 100, stability of the test media cassette after insertion into a meter (i.e. the onboard stability) needs to be in the range of 50 days. The situation, however, may be even worse considering that the patient may have a second meter and uses the present meter only from time to time. In the field of blood glucose testing, onboard stability therefore has to be shown for at least three months. It has been shown that the type of sealing as disclosed in U.S. Pat. No. 5,077,010 is insufficient to achieve the onboard stability as required in the home monitoring environment.
It is an aim of the present invention to propose body fluid testing devices and test media cassettes which contain a larger number of test media than the body fluid testing systems currently on the market and which guarantee long onboard stability of the test media. Further, it is an aim to propose meters for multiple testing which are easy to operate and which have a handheld size.